An increasing number of portable telephone units, car navigation devices and the like electronic apparatus are mounted with a light transmitting touch panel disposed at the front of a liquid crystal display panel or other display devices. Symbols and letters exhibited on the display panel can be seen through the touch panel; an operator may select and designate a specific symbol or a letter among those shown on the display panel. The operator can switch the operation of an apparatus from one function to another by pressing the touch panel with the finger or a dedicated pen at a certain specific place representing the desired function. The touch panels for use in such applications are typically required to be easy to manufacture and inexpensive.
A conventional touch panel is described with reference to FIG. 5 and FIG. 6.
For the purpose of making a clear presentation of the structural concepts, the cross sectional drawings in FIG. 5 and FIG. 6 have been shown magnified in the direction of panel thickness.
FIG. 5 is a cross sectional view which shows a conventional touch panel. In FIG. 5, light transmitting lower substrate 51 is provided at the upper surface with lower conductive layer 53 formed of indium tin oxide or other light transmitting material, while upper substrate 52 which is a light transmitting film is provided at the lower surface with upper conductive layer 54.
On the upper surface of lower conductive layer 53, dot spacers (not shown) made of an insulating resin material are disposed at a certain specific interval. A pair of upper electrodes (not shown) is provided at both sides of upper conductive layer 54, while a pair of lower electrodes (not shown) is provided at both sides of lower conductive layer 53 in the direction perpendicular to the upper electrodes.
Upper substrate 52 and lower substrate 51 are disposed so that upper conductive layer 54 and lower conductive layer 53 oppose face to face. The two substrates are coupled together with a certain specific clearance in-between using spacer 55, which spacer having the shape of a picture frame and provided at the upper surface and the lower surface with adhesive layer 56A, 56B. A finished touch panel is structured in such configuration.
FIG. 6A is a plan view of touch panels on the production line, while FIG. 6B and FIG. 6C show the cross sectional views at their production process. In the first place, adhesive layers 56A and 56B are provided, and upper release sheet 57A and lower release sheet 57B are attached to the upper surface of adhesive layer 56A and the lower surface of adhesive layer 56B, respectively. Sandwiched between them is spacer sheet 58 provided in a belt form. Out of the above material thus prepared, finished spacer 55 is obtained by cutting out spacer portion 58A, or the portion hatched to the shape of a picture frame.
Then, as shown in the cross sectional view, FIG. 6C, upper release sheet 57A and lower release sheet 57B are peeled off to have adhesive layers 56A and 56B exposed. Upper substrate 52 and lower substrate 51 are coupled together by means of spacer 55 along the circumference. Thus, a finished touch panel is provided.
A finished touch panel is disposed at the front of a liquid crystal display or other display devices to be mounted integrally on an electronic apparatus. The pair of the upper electrode and the lower electrode is connected to an electronic circuit (not shown) of the electronic apparatus.
In the above described setup, when an operator watching the display screen presses the upper surface of upper substrate 52 with the finger or a pen, upper substrate 52 is deformed bringing upper conductive layer 54 to make contact with lower conductive layer 53 at the pressed location. A voltage is applied to the upper electrode and to the lower electrode from the electronic circuit, and the electronic circuit acknowledges the pressed location by detecting the voltage ratio between the electrodes. In this way, an operator can switch the operation of the apparatus from one function to another.
Japanese Patent Unexamined Publication No. 2003-280821 is a known prior art related to the present invention.
However, spacer 55 having a picture frame shape which is used for coupling upper substrate 52 and lower substrate 51 together in the above-configured conventional touch panels is provided by making use of spacer sheet 58 only at spacer portion 58A; with the rest of the spacer sheet 58 areas, viz. inner region 58B and outer region 58C of the picture frame, left unused. The wasteful areas account for a substantial square measure as compared to that actually used for spacer 55, as shown in FIG. 6A. As a result, spacer 55 can be made available to the extent that spacer sheet 58 is used. Poor utilization rate of the material, or spacer sheet 58, in the conventional configuration has led to a problem of high cost with the touch panels.